Hydroacylation reactions of alkenes and alkynes catalyzed by transition metals are examples of the growing number of transformations which form carbon-carbon bonds based on CÀH-bond activation.[1] In particular, hydroacylation reactions offer an atom-economic entry to a variety of ketonecontaining products. [2,3] Although intramolecular reactions that afford cyclopentanones are well established, [4] access to larger ring systems [5] and intermolecular reactions remain a considerable challenge.[6] We recently described a intermolecular rhodium-catalyzed reaction based on the use of b-Ssubstituted aldehydes. [7] Although this method had advantages over previous protocols, in that the use of alkyl aldehydes under mild reaction conditions (55-65 8C) is permitted, several limitations remained. Paramount among these were the need to use electron-poor alkenes to achieve good reactivity (Scheme 1) and the use of [Rh(dppe)-(acetone) 2 ]ClO 4[4a] as the catalyst. Although this catalyst performs relatively well in intermolecular reactions, the need to generate it immediately before use from the hydrogenation of [Rh(dppe)(nbd)]ClO 4 (nbd = norbornadiene) considerably detracts from its utility.[8] We document herein the development of a highly active hydroacylation catalyst that can be Scheme 1. Intermolecular hydroacylation. dppe = 1,2-bis(diphenylphosphanyl)ethane.